[PATCH v2] scsi: pm8001: Fix data race in sysfs SAS address read

[Chengfeng Ye]

From: Chengfeng Ye <cyeaa@xxxxxxxxxxxxxx>

Fix a data race where pm8001_ctl_host_sas_address_show() reads
pm8001_ha->sas_addr without synchronization while it can be written
from interrupt context in pm8001_mpi_get_nvmd_resp().

The write path is already protected by pm8001_ha->lock (held by
process_oq() when calling pm8001_mpi_get_nvmd_resp()),
but the sysfs read path accesses the 8-byte SAS address without
any synchronization, allowing torn reads.

Thread interleaving scenario:

           Thread A (sysfs read)     |    Thread B (interrupt context)
-------------------------------------+------------------------------------
pm8001_ctl_host_sas_address_show()  |
|- read sas_addr[0..3]               |
                                     | process_oq()
                                     | |- spin_lock_irqsave(&lock)
                                     | |- process_one_iomb()
                                     | |  |- pm8001_mpi_get_nvmd_resp()
                                     | |     |- memcpy(sas_addr, new, 8)
                                     | |        /* writes all 8 bytes */
                                     | |- spin_unlock_irqrestore(&lock)
|- read sas_addr[4..7]               |
   /* gets mix of old and new */    |

Fix by protecting the sysfs read with the same pm8001_ha->lock
using guard(spinlock_irqsave) for automatic lock cleanup.

Signed-off-by: Chengfeng Ye <cyeaa@xxxxxxxxxxxxxx>
---
V1 -> V2: Use guard instead of lock/unlock pair

 drivers/scsi/pm8001/pm8001_ctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/scsi/pm8001/pm8001_ctl.c b/drivers/scsi/pm8001/pm8001_ctl.c
index cbfda8c04e95..200ee6bbd413 100644
--- a/drivers/scsi/pm8001/pm8001_ctl.c
+++ b/drivers/scsi/pm8001/pm8001_ctl.c
@@ -311,6 +311,8 @@ static ssize_t pm8001_ctl_host_sas_address_show(struct device *cdev,
 	struct Scsi_Host *shost = class_to_shost(cdev);
 	struct sas_ha_struct *sha = SHOST_TO_SAS_HA(shost);
 	struct pm8001_hba_info *pm8001_ha = sha->lldd_ha;
+
+	guard(spinlock_irqsave)(&pm8001_ha->lock);
 	return sysfs_emit(buf, "0x%016llx\n",
 			be64_to_cpu(*(__be64 *)pm8001_ha->sas_addr));
 }
-- 
2.25.1